1. Field of the Invention
The invention relates to molten metal transfer devices and, more particularly, to such a device wherein the amount of material delivered by the device can be adjusted readily and wherein components of the system can be changed readily.
2. Description of the Prior Art
Molten metal transfer devices (commonly known as shot pumps) are used to withdraw a quantity of molten metal from a bath and deliver the molten metal for purposes such as forming castings. Particularly in the casting of metals such as aluminum, shot pumps have included a chamber disposed within a bath of molten metal. The chambers have been oriented generally vertically and cup-like buckets have been disposed within the chambers for reciprocating vertical movement. The chambers have included appropriate openings such that molten metal from the bath can flow into the chamber and into the bucket; upon raising the bucket, molten metal carried by the bucket can be lifted to a location where the metal can be discharged from the chamber for transfer to casting equipment.
Although prior shot pumps have enabled molten metal to be removed from a bath in separate, small quantities, certain problems have not been addressed. One of these problems relates to precisely controlling the amount of material withdrawn from the bath with each cycle of the pump. One known prior shot pump employs a wedge-shaped piston disposed within a cylinder. Molten metal is permitted to flow into the cylinder and accumulate atop the piston. Thereafter, upon raising the piston, molten metal trapped above the piston is lifted upwardly and can be discharged outwardly from the cylinder. Unfortunately, the shape of the piston and various other parameters of the pump make it very difficult to adjust, with any degree of accuracy, the amount of material delivered with each cycle of the pump.
Another known device employs a cup-like bucket having an opening formed near the bottom of the bucket. When the bucket is raised to a certain position within a chamber, molten metal carried by the bucket is permitted to flow outwardly through the opening. As with the earlier described device, the amount of material carried by the bucket and ultimately discharged from the bucket is very difficult to control.
Another problem not addressed by proper shot pumps is that of a proper relationship between the size of the bucket and the chamber within which the bucket is disposed. In prior pumps, if a close-fitting relationship has been provided between the bucket and the chamber, adequate sealing characteristics will be provided, but excessive wear may occur and it will be difficult, if not impossible, for the bucket to be removed from the chamber and replaced from time to time. On the other hand, if a loose-fitting relationship between the bucket and the chamber is provided, adequate sealing characteristics will not be available.
Additional problems not addressed by prior shot pumps include the capability of removing the bucket from the chamber and replacing it quickly with another bucket. Prior shot pumps have required considerable down-time and reconfiguration of the pump in order to make such a change. Yet an additional problem not addressed by prior shot pumps is that of changing a chamber and bucket assembly when it is desired to significantly alter the quantity of metal being removed from the bath.